Method of measuring point-blank passing time or the like of airplane

ABSTRACT

A terrain clearance measuring radio wave being emitted from an airplane is received, and changes in electric field intensity of the radio wave is input and recorded to a computer, whereby the time of occurrence of a sharply appearing peak value of the changes permits accurate measurement of the point-blank passing time, independent of flight frequency.

TECHNICAL FIELD

[0001] The invention relates to a method for measuring, at one spot onthe ground, the point-blank passing time at which an airplane flyingthrough the overhead sky comes closest to the spot, and a method formeasuring the flight position, flight direction, and flight course ofthe airplane, and the sound noise produced by the airplane, using theabove described method.

BACKGROUND ART

[0002] Accurate collecting of point-blank passing time of an airplanepassing through the overhead sky at one spot on the ground is anessential basic requirement for increasing measurement accuracy whenvarious measurements are performed on the airplane.

[0003] In conventional measurement of point-blank passing time,point-blank passing time is usually estimated by removing noisecomponents from data on changes in sound noise level, obtained bymeasuring airplane-produced sound noise, with reference to the time whenthe peak value of the change of sound noise level is collected, andfurther by taking into account the weather and meteorological conditionsand the like.

[0004] Further, in measuring the above described airplane sound noise,by receiving a transponder response signal radio wave of 1090 MHz whichis emitted from the airplane and non-directional in horizontal plane,and by examining the correlations between the changes in the electricfield intensity level of the radio wave and the airplane modelidentification data and flight height data obtained by decoding thetransponder response signal, it has been possible to accurately measurethe point-blank passing time based on the time when the peak value ofelectric field intensity is collected (Japanese Patent Laid-Open No.4-40646).

[0005] In a conventional method for measuring point-blank passing timeaccording to the above described airplane-produced sound noisemeasurement, the method requires taking into account complicatedvariable factors to perform a cumbersome task of data analyses, andfurther the measurement accuracy is insufficient and thus not completelysatisfactory.

[0006] Also, in a method for measuring the point-blank passing timeaccording to both the sound noise measurement and the peak value of theelectric field intensity level of the transponder response signal radiowave, the measurement can be performed with considerable accuracy.However, the peak value of the transponder response signal radio waveitself is flat in time distribution, thus causing a problem thatsufficient accuracy can not be achieved.

[0007] Recent airplane flights are significantly increased in number,and particularly the number of airplanes taking off from and landing toan airport can be more than 500 per a day. In the surroundings of theairport, flight density can be so high that the flight interval may beless than 90 seconds, resulting in serious pollution ofairplane-produced sound noise.

[0008] In the case of such a high frequency of flight, the measuring ofpoint-blank passing time according to the above described soundnoise-measuring means is difficult to identify individual airplanes andtherefore virtually produce no effect. Also, the means for receiving thetransponder response signal radio wave has a problem that it is almostimpossible to collect the peak value of electric filed intensity of theradio wave.

DISCLOSURE OF THE INVENTION

[0009] The invention provides a method for measuring point-blank passingtime by receiving, at a measuring point on the ground, a terrainclearance measuring radio wave downwardly directed and emitted from anairport, and inputting to a computer changes in electric field intensitylevel of the radio wave.

[0010] Airplanes are provided with one to three radio wave-transmittingantenna(s) for terrain clearance measurement, which antenna has sharpdirectivity directed directly downward and is mounted on the bottomsurface of the bodyworks thereof. They are flying while emitting adirective radio wave of a sweep signal of 4.3 GHz (in the case ofmilitary airplanes, a pulse signal of a frequency band equal to or morethan 4.3 GHz), which radio wave is shaped into an emission patternspreading usually 30° in the forward direction, 20° in the backwarddirection and 50° to 60° in the right—to —left direction, though thesevalues are different depending on airplane models.

[0011] Therefore, by receiving the above described terrain clearancemeasuring radio wave at one spot on the ground, and inputting andrecording to a computer changes in electric field intensity level of theradio wave, it is possible to obtain a waveform of changes in theelectric field intensity level while the emission pattern of the terrainclearance measuring radio wave emitted from the airplane is crossingthrough the above described spot. At this time, the peak value of thewaveform indicates that a vertical plane perpendicular to the flightdirection and including the directly downward axis of the airplane haspassed the above described spot, and the time corresponding to the peakcan be regarded as the point-blank passing time.

[0012] If the airplane has passed through the sky directly above themeasuring point, the length of time required for collecting the changesin electric field intensity level is long and the peak value intensityalso becomes highest. However, as the flight path is distant in thesideward direction from the path directly above the spot, the length ofdata-collecting time required becomes short and the peak value intensityalso becomes low. Further, the collecting range, collecting time, peakvalue intensity and the like also change depending on the flightaltitude.

[0013] However, the rising to and the falling from the peak value arevery abrupt, and therefore point-blank passing time can be accuratelymeasured as long as the peak value can be collected.

[0014]FIG. 9 shows a printed out graph of changes in electric fieldintensity level of the terrain clearance measuring radio wave and thetransponder response signal radio wave over 30 minutes, which changesare obtained by receiving both waves of an airplane rising at analtitude of about 700 m above a spot surrounded by a forest area, whichis located directly below the takeoff air route and 5 km away in thedirection of north from the north end of the runway of Narita airport.Although the received peak values of the terrain clearance measuringradio wave according to the invention are very sharp, the peak valuesaccording to the transponder response signal radio wave are so broad atthe points of peak values that the peak points are unclear.

[0015]FIG. 10 shows comparison data similar to the case of FIG. 9,obtained with respect to an airplane descending at an altitude of about1500 m above a spot, which is located directly below the landing airroute and 20 km away in the direction of south from the south end ofNarita airport. Because the spot is located at seaside and can offer acomplete view of the overhead sky, the transponder response signal radiowaves from many airplanes flying over the wide range are superimposedand received. Therefore, those radio waves are always received at highlevel, and thus it is difficult to identify individual received signals,and it is needless to say that individual peak values become entirelyunknown. In contrast to this, the terrain clearance measuring radio waveaccording to the present invention is collected clear and sharp in thesame manner as in the case of FIG. 9.

[0016] The examples of measurement of the above described transponderresponse signals show the cases in which both radio waves are receivedby non-directional antennas. However, in the case of targeting an airroute where the flight direction and path of flying airplanes areapproximately constant, when reception area is limited by the use ofunidirectional antenna, it is possible to collect the response signalfor each airplane. Then, the response signal is useful as approachinformation, but it is insufficient in measurement accuracy aspoint-blank passing information because the peak value of the responsesignal is flat in width and particularly the directivity of thetransponder antenna mounted on an airplane becomes null (sensitivity ofzero) in the directly downward direction of the airplane.

[0017] The invention is for measuring accurate point-blank passing timeby using a terrain clearance measuring radio wave downwardly directedand emitted from an airplane, but the invention also allows receivingthe radio wave by a directly-upward-directional antenna to limit ameasured area. Particularly because the terrain clearance measuringradio wave is horizontally polarized with respect to the flightdirection, receiving the radio wave by a unidirectional polarizationantenna permits the reception area of radio wave to be limited to anarea extending along a main air route. For example, in the case of anairport having parallel runways, a plurality of polarization antennascorresponding to each runway are divided into the respective runways,thereby permitting the automatic measuring of the passing times, thenumber of passing airplanes, flight intervals and the like with respectto airplanes taking off or landing.

[0018] The directivity characteristic of the above describedunidirectional polarization antenna is already known. For example, thedirectivity coefficient D of a λ/2 dipole type of polarization antennacan be calculated by the following equation,

D(θ)=cos(π/2·cos θ)/sin θ,

[0019] and the directivity characteristic diagram thereof can bedisplayed as an elliptical figure in which the directivity axis is takenas the major axis (see FIG. 6).

[0020] Therefore, a plurality of unidirectional polarization antennas ofthe λ/2 dipole type are combined and placed such that at least one ofthe antennas may have the directivity axis directed directly upward andthe others each may have different directions of directivity axis and/ordifferent receiving polarization planes. Thereby, it is possible toobtain the basic data of azimuth direction with respect to the spatialposition of the airplane at this time at the measuring point, data ofazimuth angle, and data of flight direction of the airplane, togetherwith the point-blank passing time of airplanes.

[0021] For example, as shown as antennas A and B in FIG. 1, twopolarization antennas (a1, a2) of a λ/2dipole type are combined suchthat the antennas may both have directly-upward vertical directivityaxes and both element axes of the antennas are horizontally orthogonalto each other so as for the receiving polarization planes to beorthogonal to each other. In this combination, when the antennasreceives the terrain clearance measuring radio wave of an airplane, thesignal outputs of both antennas exhibit peak values at the point-blankpassing time of the airplane, and the ratio between the respectiveintensity peak values indicates a specific numerical value of thedirectivity coefficient value ratio shown in Table 1, which numericalvalue is dependent on the azimuth angle with respect to the spatialposition of the airplane at that time.

[0022] For example, when the polarization antenna a1 gives a peak valueand the polarization antenna a2 senses nothing, the airplane position islocated in the azimuth of the directivity axis of the antenna a1. Whenthe ratio between the output values of a1 and a2 is 1, the airplaneposition is located in the direction of the azimuth angle of either 45°or 135° with respect to the directivity axis directions of the antennas.When the output ratio is a value other than these, it is indicated thatthe airplane is located at an azimuth angle other than the abovedescribed angle according to the ratio.

[0023]FIG. 6 is a diagram for showing the directivity characteristics ofboth antennas a1 and a2 in this case, and Table 2 is a table for showingthe ratio between both directivity coefficient values according to therespective directivity coefficient values of both antennas and thearrival direction of the radio wave. Based on this table, it is possibleto obtain basic data on azimuth angles with respect to the spatialposition of an airplane.

[0024] Further, two polarization antennas a1 and a2 of a λ/2 dipole typeare combined such that the pole elements of both antennas may behorizontal and parallel to each other so as for both receivingpolarization planes to coincide with each other, and the antenna a1 hasthe directivity axis directed directly-upward in the vertical directionand the antenna a2 has the directivity axis inclined 30° toward the skywith respect to the vertical axis. In the this case, the directivitycharacteristic diagram is given as shown in FIG. 7, and the directivitycoefficient values and the ratio between both coefficient values arespecified according to the spatial position of airplanes, as shown inTable 2.

[0025] Therefore, the point-blank passing time of the airplane can bemeasured by the time when the antenna a1 gives a peak value, and alsothe elevation angle with respect to the airplane position at themeasuring point at that time can be obtained by the ratio between theoutput value of the antenna 2 at this time and the output value of theabove described peak value.

[0026] A receiving device comprising the above described combination oftwo polarization antennas is useful mainly for measuring the passingtime and the number of passing airplanes with regard to the passage ofairplanes flying along a given air route. However, a plurality of thesetwo antenna combinations can be combined to expand the measurable skyarea and achieve the increased degree of measuring accuracy of theflight traveling direction and traveling azimuth angle of airplanes.

[0027] For example, in contrast to the set of the above described twopolarization antennas a1 and a2 which each have polarization planesorthogonal to each other and directly-upward vertical directivity, ifthe antenna a1 and a2 each have directivity inclined toward the overheadsky in the four directions with respect to the vertical axis and each ofthe antennas a1 and a2 is combined with four polarization antennas whichhave receiving polarization planes overlapped with the receivingpolarization planes of the antennas a1 and a2, that is, use of a total10 channel type of receiving device, it is possible to performmeasurement adaptable to all flight directions.

[0028] However, in this case, processing of data received by the 10channels becomes complicated, thereby causing a problem of increasedcost of the receiving device and computer equipment.

[0029] Practically, 6 polarization antennas are combined and placed toconfigure a 6 channel type of receiving device, wherein two of them havedirectly-upward directivity axes and polarization planes orthogonal toeach other, and other four antennas have the same receiving polarizationplane as one of the above described directly-upward-directional antennasand are inclined such that their directivity axes may be respectivelyspread out toward the overhead sky so as to divide the sky into fourparts. Thus, the 6 channel type of receiving device inputs, to acomputer, respective changes in electric field intensity level of theterrain clearance measuring radio wave of an airplane, whereby togetherwith the point-blank passing time of the airplane, data on the azimuthangle and elevation angle with respect to the spatial position of theairplane at that time as well as the flight traveling direction thereofcan be measured. This measurement can be economically and effectivelyperformed mainly for measuring airplanes flying along a prescribed airroute.

[0030] Further, the time for measuring an airplane model identifyingsignal obtained by receiving a transponder response signal transmittedfrom the airplane and the respective data obtained by flight altitudemeasurement and sound noise measurement is tailored to coincide with themeasurement of the above described point-blank passing time obtained byreceiving the terrain clearance measuring radio wave. Thereby,reliability of various measurements on individual airplanes can beincreased, and particularly selecting of airplane-produced sound noisefrom the sound noise can be very accurately and easily performed.

[0031] In this case, the receiving point for the terrain clearancemeasuring radio wave, the receiving point for the transponder responsesignal, and the measuring point for the sound noise may be the same spotor different spots separated from each other.

[0032] Then, a plurality of measuring points for point-blank passingtime are distributed and provided, with 2-4Km spacing provided betweenthe measuring points, on the ground including an area located directlybelow the air route. Further, a plurality of sound noise-measuringpoints are distributed and arranged at required positions between thepoint-blank passing time-measuring points, and furthermore a transponderresponse signal-receiving point is provided at an arbitrary spots. Inthis manner, the data measured at those spots are collected to a centralaggregation office, thereby permitting accurate and easy measurement ofthe flight conditions, flight courses and the like of airplanes and thesituations of distribution of sound noise produced over a given area bythe airplanes.

[0033] In the present invention, the changes in electric field intensitylevel of the terrain clearance measuring radio wave obtained by thedirectly-upward-directional antenna shows intensity change starting tobe received 5 to 10 seconds before the point-blank passing time ofairplanes and abruptly rising about 2 to 3 seconds before the passingtime, wherein the airplane are at an altitude equal to or less than 2000m and have the potential for effecting sound noise on the measuringpoint. Therefore, a camera having a photography field directed in thedirectly-upward direction is provided at a spot located directly belowthe air route and the time of its initiation is controlled by using, asthe trigger, a given intensity value of the rising electric fieldintensity of the terrain clearance measuring radio wave, therebypermitting easy collection of effective airplane passage records.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]FIG. 1 is a plan view for showing a combination and placement ofsix polarization antennas according to a first embodiment;

[0035]FIG. 2 is a side view for showing the placement of the fourpolarization antennas taken along a line x-x of FIG. 1;

[0036]FIG. 3 is a side view for showing the placement of the threepolarization antennas taken along a line y-y of FIG. 1;

[0037]FIG. 4 is a block diagram for showing an electric fieldintensity-measuring circuit for a terrain clearance measuring radiowave;

[0038]FIG. 5 is a display diagram for showing a printout of data inputand recorded to computer;

[0039]FIG. 6 is a directivity characteristic of two polarizationantennas of a λ/2 dipole type which are combined to be orthogonal toeach other;

[0040]FIG. 7 is a directivity characteristic of two polarizationantennas of a λ/2 dipole type which are combined to form 30° betweentheir directivity axes;

[0041]FIG. 8 is a display diagram for showing the position and flightdirection of an airplane at the point-blank passing time depicted on amap, based on the recorded data of FIG. 5;

[0042]FIG. 9 is an arrangement diagram for showing four point-blankpassing time-measuring points along an air route and five soundnoise-measuring points located in between the measuring points accordingto a second embodiment;

[0043]FIG. 10 is an edit diagram for showing video camera-photographedframe pictures of an airplane flying through the overhead sky accordingto a third embodiment;

[0044]FIG. 11 is a display diagram for showing changes in electric fieldintensity levels of the terrain clearance measuring radio wave andtransponder response signal radio wave of an airplane when both wavesare received at the same time; and

[0045]FIG. 12 is a display diagram similar to FIG. 11 for showing thecase of changed measuring points.

DESCRIPTION OF SYMBOLS

[0046] A, B, C, D, E, F: Polarization antenna

[0047] P: Element axis

[0048] H: Flight altitude

[0049] M: Point-blank position

[0050] O: Point-blank passing time-measuring point

[0051] S: Sound noise-measuring point

[0052] R: Prescribed air route

[0053] Z: End of runway

Best Aspect for Carrying Out the Invention

[0054] Aspect 1

[0055] A six channel type of receiving device is fixedly mounted on theupper end of a 2 m high column provided at a spot located about 5 kmaway in the direction of north from the north end of the runway ofNarita airport, wherein the receiving device has six polarizationantennas combined according to the conditions shown in FIG. 1 forreceiving the terrain clearance measuring radio wave of an airplane.Also, an antenna for receiving the transponder response signal radiowave is mounted on the side of the column. Changes in electric fieldintensity levels of the radio waves are input and recorded to a computervia a circuit shown in a block diagram of FIG. 4 by the respectiveantenna-received signals.

[0056]FIG. 5 shows the printout of the recorded changes of each data.

[0057]FIG. 1 is a plan view for showing the combination and placement ofsix polarization antennas of a λ/2 dipole type which antenna is toreceive a 4 GHz band for the terrain clearance measurement and has ahalf-value angle width of about 80°. FIG. 2 is a side view for showingthe placement condition along an axis x-x of FIG. 1, and FIG. 3 is aside view for showing the placement condition along an axis y-y of FIG.1.

[0058] Antennas A and B are of vertical directly-upward-directeddirectivity and are placed such that their element axes P have thepolarization planes orthogonal to each other in the horizontaldirection, and antennas C, D, E, and F surround the vertical axis andare each inclined 30° with respect to the vertical axis to havedirectivity directed toward the overhead sky in the four directions ofeast, north, west and south, wherein the element axes P of the antennasD and F and the antenna A are horizontal and parallel, and the elementaxes P of the antennas C and E are the same in the direction oforientation as the antenna A and are each inclined 30° in the oppositedirection.

[0059]FIG. 5 is a graph with a horizontal axis indicating time and avertical axis indicating electric filed intensity values and flightaltitude, for showing the printout of data input and recorded to acomputer, wherein the x-x axis of the above combined antennas lies inthe direction of south-north at a measuring point, and the above dataincludes the changes in electric field intensity level obtained byreceiving a terrain clearance measuring radio wave emitted from anairplane flying through the overhead sky above a measuring point, andthe flight altitude information obtained by decoding the transponderresponse signal radio.

[0060] From the graph of FIG. 5, the respective times at which thedirectly-upward-directional antennas A and B gives peak valuesapproximately coincide with each other, showing the point-blank passingtime of an airplane. The ratio (A/B) between the respective peak valuesA 820 and B 230 is 3.562. Thus, Table 1 shows that the azimuth anglewith respect to the arrival direction of the radio wave is 19° or 341°,indicating that the airplane is located in either direction of theseangles at the point-blank passing time. Further, each output value ofthe antennas C (east), D (north), E (west), and F (south) inclined anddirected in the four directions is related as E>D>C>F at the point-blankpassing time, indicating that the airplane is located in the west southdirection from the measuring point O, and it can be known that theairplane is located in the vertical plane including the direction of anazimuth angle of 19°+180° from the measuring point. Further, because theoutput values are related as E≈D>F>C about 3 seconds before thepoint-blank passing time and as F≈E >C>D about 3 seconds after thepoint-blank passing time, it can be known that the airplane passedthrough the point-blank position from northwest and then flied toward inthe direction of east-southeast. Also, the intensity ratio between thepeak value 820 of A at the point-blank passing time and the output value1180 of the antenna E at that time is 0.695, and therefore it can beknown from Table 2 that the elevation angle with respect to the airplaneat the point-blank position is about 42°, and the altitude of theairplane is known about 540 m by decoding the transponder responsesignal at that time.

[0061] From the above data, it can be known that the air plane islocated at the position of an azimuth angle 199, elevation angle 42, andan altitude 540 m with respect to the measuring point O, and the aboveposition is a straight distance of 810 m, and a horizontal distance of600 m on the ground plane, from the measuring point, and that the flightdirection of the airplane heads from west-southwest to east-southeast atan azimuth angle 109° orthogonal to a vertical plane including the abovedescribed azimuth angle.

[0062]FIG. 8 is a display diagram for showing the position and flightdirection of the airplane at the point-blank passing time depicted on amap, based on the above data.

[0063] Aspect 2

[0064] As a sound noise-measuring system covering an area including azone located directly below a 12 km long, straight air route extendingin the north direction from the north end of the runway of Naritaairport, as shown in FIG. 9, the same receiving and measuring points O1to O4 for the terrain clearance measuring radio wave as in the firstembodiment are provided at four spots located approximately along anddirectly below the prescribed air route R, and sound noise-measuringpoints S1 to S6 are provided at six spots in between the receiving andmeasuring points, and thus the measurement data obtained at eachmeasuring point is collected to a central aggregation office, wherebyrequired data in accordance with an object is obtained as follows.

[0065] Usually, airplanes taking off from and landing to an airport arecontrolled to fly within an allowed area including both side zoneshaving a predetermined lateral distance and extending along a prescribedair route, and the width of the allowed area is 500 m in the lateraldirection at a position 5 km away from the end of the runway, and 1000 mat a position 10 km.

[0066] Therefore, based on each point-blank passing time measured at themeasuring points O1 to O4 and distances between the measuring points, anaverage horizontal speed of an airplane can be calculated. Further, thepoint-blank passing time at each sound noise-measuring point also can beaccurately estimated based on a distance between a measuring point O anda spot where the normal from the sound noise-measuring point to theprescribed air route intersects to the air route. Therefore,identification and extraction of airplane-produced sound noise out ofthe data of sound noise measurement forming a complicated waveform canbe accurately and easily performed with reference to the passing time.

[0067] In this example, each space distance of the runway endZ˜O1˜O2˜O3˜O4 is 4087 m, 2092 m, 2659 m, 1996 m, respectively, and thecorresponding flight times are 66 seconds in the predicted value basedon data base for the space distance of the runway end Z˜O1, and 21seconds, 24 seconds, 23 seconds in measured values for the spacedistances O1˜O2˜O3˜O4, respectively. Therefore, the average horizontalspeeds for the respective space distances are calculated as 60 m/second,99.6 m/second, 110.8 m/second, and 88.8 m/second, respectively. Based onthis, the point-blank passing times at each of the sound noise-measuringpoints S1 to S5 located between the measuring points can beapproximately accurately calculated.

[0068] Further, in the case of the above described case, when flightmodel-identifying data and altitude signal data obtained by reception ofthe transponder response signal collected at an arbitrary spot arecombined with data of an azimuth angle and elevation angle with respectto the arrival direction of the terrain clearance measuring radio waveat each point-blank passing time at each of the measuring points O1 toO4, it is also possible to measure the flight position and flightdirection of the airplane at each measuring point. Further, these dataobtained at each measuring point can be comprehensively computed at acentral aggregation office to calculate an accurate flight course,thereby providing reliable materials for flight management and materialsfor countermeasures against airplane-produced sound noise.

[0069] Aspect 3

[0070]FIG. 12 shows a photographic record shot by a camera, of whichfield of view is a given range of the overhead sky having its centerlocated directly above a measuring point, according to an embodiment ofa method of photographing at the point-blank passing time, wherein, whenchanges in electric field intensity level of a terrain clearancemeasuring radio wave emitted in the aeronautical area is received by areceiving antenna having directivity directed in the directly-upwarddirection of the spot and is then input and recorded to a computer, thecamera is initiated by a trigger signal of a predetermined intensityvalue in the rising process of the electric field intensity.

[0071] This record is a time series edition of a {fraction (1/30)}second frame exposure portion of takeoff airplane pictures taken by avideo camera provided at a measuring point, which point is locateddirectly below the air route and 7 km away in the north direction fromthe north end of the runway of Narita airport. According to sevenairplane pictures recorded from 20 minutes past 13 o' clock to 56minutes at the same o' clock Sep. 12, 2000, each airplane passed throughthe sky a little apart in the direction of west from the sky directlyabove the measuring point, and the airplane models, flight directions,and flight altitudes can be estimated from the shapes and sizes of theairplane pictures, which are useful as on-target airplane passagerecords.

Industrial Applicability

[0072] According to the invention, the measuring of the point-blankpassing time with respect to an overhead passing airplane is performedby receiving a terrain clearance measuring radio wave directed directlydownward from the airplane, and inputting and recording changes inelectric field intensity level of the radio wave, and using the timewhen a peak value of the changes is produced. Therefore, as comparedwith a conventional method based on the measured value of sound noiseand the value of electric field intensity of a transponder responsesignal radio wave, more accurate and reliable measurement can beperformed. Particularly, in the case of high flight frequency wheremeasurement by the prior art method is almost impossible or veryinferior in accuracy, the present invention allows accurate measurementof the point-blank passing times of the individual airplanes.

[0073] Based on this accurate measurement of point-blank passing time,it is possible to recognize flight conditions of an airplane bycombining the directivity characteristics of a plurality of antennas forreceiving the terrain clearance measuring radio wave, and bysimultaneously using sound noise-measuring means and transponderresponse signal-decoding means together with the combined antennas, itis possible to increase accuracy in various measurements on theairplane. In addition, by scattering and distributing these measuringpoints on the ground and, if required, distributing and placing soundnoise-measuring points between the measuring points, collecting thesedata to the central aggregation office it is possible to obtain flightcontrol materials such as reliable flight course and the like or basicmaterials for countermeasures against airplane-produced sound noise overa given area.

[0074] Further, the invention may be used as invasion alarming means forabnormal path not following air traffic control and a suspiciousairplane in low-altitude flight. TABLE 1 Angle Antenna a1 Antenna a2a₁:a₂ 0 1.0000 0.0000 2 0.9991 0.0274 36.4393 4 0.9964 0.0549 18.1654 60.9920 0.0823 12.0502 8 0.9858 0.1098 8.9751 10 0.9779 0.1374 7.1164 120.9683 0.1651 5.8662 14 0.9571 0.1928 4.9642 16 0.9443 0.2206 4.2801 180.9300 0.2485 3.7418 20 0.9143 0.2766 3.3058 22 0.8971 0.3047 2.9447 240.8787 0.3329 2.6399 26 0.8591 0.3611 2.3789 28 0.8383 0.3894 2.1526 300.8165 0.4178 1.9543 32 0.7937 0.4462 1.7790 34 0.7700 0.4745 1.6229 360.7456 0.5028 1.4830 38 0.7204 0.5309 1.3569 40 0.6946 0.5589 1.2428 420.6683 0.5867 1.1390 44 0.6415 0.6143 1.0443 46 0.6143 0.6415 0.9576 480.5867 0.6683 0.8780 50 0.5589 0.6946 0.8046 52 0.5309 0.7204 0.7370 540.5028 0.7456 0.6743 56 0.4745 0.7700 0.6162 58 0.4462 0.7937 0.5621 600.4178 0.8165 0.5117 62 0.3894 0.8383 0.4646 64 0.3611 0.8591 0.4204 660.3329 0.8787 0.3788 68 0.3047 0.8971 0.3396 70 0.2766 0.9143 0.3025 720.2485 0.9300 0.2673 74 0.2206 0.9443 0.2336 76 0.1928 0.9571 0.2014 780.1651 0.9683 0.1705 80 0.1374 0.9779 0.1405 82 0.1098 0.9858 0.1114 840.0823 0.9920 0.0830 86 0.0549 0.9964 0.0551 88 0.0274 0.9991 0.0274 900.0000 1.0000 0.0000

[0075] TABLE 2 Angle Antenna a1 Antenna a2 a₁:a₂ 0 1.0000 0.8165 1.22472 0.9991 0.8383 1.1918 4 0.9964 0.8591 1.1599 6 0.9920 0.8787 1.1289 80.9858 0.8971 1.0989 10 0.9779 0.9143 1.0695 12 0.9683 0.9300 1.0412 140.9571 0.9443 1.0135 16 0.9443 0.9571 0.9866 18 0.9300 0.9683 0.9605 200.9143 0.9779 0.9349 22 0.8971 0.9858 0.9101 24 0.8787 0.9920 0.8858 260.8591 0.9964 0.8622 28 0.8383 0.9991 0.8391 30 0.8165 1.0000 0.8165 320.7937 0.9991 0.7944 34 0.7700 0.9964 0.7728 36 0.7456 0.9920 0.7516 380.7204 0.9858 0.7308 40 0.6946 0.9779 0.7103 42 0.6683 0.9683 0.6902 440.6415 0.9571 0.6702 46 0.6143 0.9443 0.6505 48 0.5867 0.9300 0.6309 500.5589 0.9143 0.6113 52 0.5309 0.8971 0.5918 54 0.5028 0.8787 0.5722 560.4745 0.8591 0.5523 58 0.4462 0.8383 0.5322 60 0.4178 0.8165 0.5117

1. A method for measuring the point-blank passing time of an airplane,characterized by continuously receiving a terrain clearance measuringradio wave downwardly directed and emitted from the airplane flyingthrough the overhead sky at one spot on the ground, and inputting andrecording to a computer changes in electric field intensity level of thewave.
 2. The method for measuring the point-blank passing time of anairplane according to claim 1, wherein the reception of the terrainclearance measuring radio wave is performed by an antenna which ishorizontally non-directional and directly-upward directional.
 3. Themethod for measuring the point-blank passing time of an airplaneaccording to claim 1, wherein a receivable area of the terrain clearancemeasuring radio wave is limited to one direction by a polarizationantenna which is horizontally unidirectional and directly-upwarddirectional.
 4. The method for measuring the point-blank passing time ofan airplane according to claim 1, wherein the receiving of the terrainclearance measuring radio wave is performed by combining twopolarization antennas each having horizontally unidirectional anddirectly-upward directional directivity such that the elements axes ofthe antennas may be orthogonal to each other or may obliquely intersect,and wherein the changes in electric field intensity received by each ofthe two antennas are input and recorded to a computer at the same time,thereby providing basic data on an azimuth angle with respect to theposition of the airplane at the point-blank passing time.
 5. The methodfor measuring the point-blank passing time of an airplane according toclaim 1, wherein the reception of the terrain clearance measuring radiowave is performed by combining and placing six polarization antennas,wherein two antennas of the antennas have directly-upward-directeddirectivity and the element axes orthogonal to each other in thehorizontal direction, and the other four antennas have the element axesconformed to the element axis of one of said directly-upward-directeddirectivity antennas in the direction of orientation and are inclinedsuch that their axes of directivity, surrounding the directly upwardaxis, may be respectively spread out toward the overhead sky so as todivide the sky into four parts, and the respective changes in electricfield level received by the six antennas are input to the computer atthe same time, thereby providing an azimuth angle and elevation angle aswell as flight direction data with respect to the flight position of theairplane at the point-blank passing time.
 6. A method for measuring thepoint-blank passing time and sound noise of an airplane, characterizedin that together with changes in electric field intensity level obtainedby continuously receiving a terrain clearance measuring radio wavedownwardly directed and emitted from said airplane flying through theoverhead sky at one spot on the ground, airplane model identifyingsignal information and flight altitude information obtained by receivingand decoding a transponder response signal radio wave emitted from saidairplane at the same time at the same spot or a different spot and/orsound noise data from said airplane measured at the same spot or adifferent spot are input and recorded to a computer.
 7. A method forestimating the point-blank passing time of an airplane, characterized byinputting and recording, to a computer of a central aggregation office,data on changes in electric field intensity level obtained bycontinuously receiving a terrain clearance measuring radio wavedownwardly directed and emitted from an airplane flying through theoverhead sky at each of a plurality of spots scattered and distributedon the ground plane, wherein the point-blank passing time of saidairplane at an intermediate spot other than said measuring points isestimated.
 8. A method for measuring a flight course of an airplaneand/or noise produced by the airplane, characterized by inputting andrecording to a computer of a central aggregation office, together withdata on changes in electric field intensity level obtained bycontinuously receiving a terrain clearance measuring radio wavedownwardly directionally emitted from the airplane flying through theoverhead sky at each of a plurality of scattered and distributed pointson the ground surface, an airplane model identifying signal and flightaltitude information data obtained by continuously receiving atransponder response signal emitted from the airplane at the same pointor a different point at the same time, and/or noise data obtained at thesame point or a different point at the same time.
 9. A method forphotographing an airplane at the point-blank passing time characterizedin that, in conjunction with the inputting and recording, to a computer,of changes in electric field intensity level obtained by continuouslyreceiving a terrain clearance measuring radio wave downwardly directedand emitted from an airplane flying through the overhead sky at one spoton the ground, a camera for photographing a given range of the skydirectly above the spot is initiated when the electric field intensitylevel reaches to a given value.